1. Field of the Invention
The present invention relates to a method for controlling the shrinkage of a formed ceramic body during firing and, more particularly, to a method for controlling the shrinkage of a formed ceramic body when a ceramic product is manufactured by a predetermined manufacturing process from ceramic powder produced by grinding using a dry-type ball mill such as an Attritor.
2. Description of Related Art
To increase the accuracy of dimension and shape of finished products and to avoid defects in the shape and the like in the manufacture of ceramic products, it is important to control the degree of firing shrinkage when a formed body is produced from a raw material such as a ceramic powder and is fired to obtain a fired body. Particularly, in the context of electronic parts such as ICs and condensers, in which multi-layer ceramic substrates are used, controlling the shrinkage of the green sheets used for the multi-layer ceramic substrates is very important.
FIG. 5 is a process flow diagram showing a process for manufacturing green sheets for multi-layer ceramic substrates. In this manufacturing process, ceramic powder procured by purchasing and is ground using attritor (hereinafter referred to as a dry-type ball mill). The ground ceramic powder is taken out from the ball mill and treated with heat.
Next, a binder, a dispersant, a plasticizer, and the like are added to the ground ceramic powder. Then, a liquid such as butanol is further added and the resulting material is mixed using a trommel mixer.
The slurry obtained in this manner is molded into a formed body (a green sheet) with predetermined dimensions using a doctor blade forming machine. The formed body is then dried and fired.
Conventionally, a commonly accepted method of controlling the firing shrinkage in the process for manufacturing ceramic products has been to suppress fluctuation of the shrinkage by constantly employing fixed manufacturing conditions (no specific prior art document has been found on this subject). As specific manufacturing conditions in the process for manufacturing green sheets, for example, heat treatment conditions for treating ground ceramic powder with heat (heating temperature, heating time, etc.), the composition of compounded ingredients (the amount of a dispersant, etc.), raw material mixing conditions (mixing time, etc.), formed body drying conditions (temperature, air flow rate, etc.), press conditions (temperature, mass, etc.), formed body firing conditions (firing temperature, firing time, etc.), and the like can be given. It has been a conventional practice to maintain all of these conditions constant for controlling the shrinkage.
However, even if all of these conditions in the process of manufacturing ceramic products are maintained constant, the shrinkage significantly fluctuates according to the lot of ground ceramic powder used. Thus, it has been difficult to accurately control the shrinkage by conventional controlling methods.
The present invention has been completed in view of this situation and has an object of providing a method for controlling the shrinkage of formed ceramic bodies, by which it is possible to suppress fluctuation of the shrinkage of formed ceramic bodies and to cause the shrinkage amount to approximate a target rate.